The high gain required for oscillation in semiconductor lasers results in a large optical bandwidth in which laser operation is possible. This large bandwidth generally results in multiple-longitudinal-mode operation. For many applications, single-longitudinal-mode operation is required. Consequently, sophisticated structures such as the distributed feedback (DFB) laser [see D. R. Scifres, R. D. Burnham, and W. Streifer, Appl. Phys. Lett. 25, 203 (1974)] and the cleaved-coupled-cavity (C.sup.3) laser [see W. T. Tsang, Lightwave Communications Technology, Part B, Semiconductor Injection Lasers, I, edited by W. T. Tsang, in Semiconductors and Semimetals, Vol. 22, edited by R. K. Willardson and A. C. Beer (Academic, Orlando, 1985), Chap. 5, pp. 257-373] have been developed to ensure single-mode operation. The DFB laser employs a fine-scale periodic corrugation of relatively small index steps to interact with the electromagnetic wave. The C.sup.3 laser relies on several large-scale nonperiodic monolithic cavities for feedback and mode selection.
It is among the objects of the present invention to provide a semiconductor laser that can exhibit desirable single mode operation and can be fabricated using relatively simple techniques.
Optical switching and bistability are important for applications such as optical memories, optical signal processing, and optical logic elements. A variety of semiconductor laser devices have exhibited switching and bistability, including: lasers with saturable absorbers [see M. I. Nathan, J. C. Marinace, R. F. Rutz, A. E. Michel, and G. J. Lasher, J. Appl. Phys. 36, 473 (1965); C. Harder, K. Y. Lau, and A. Yariv, IEEE J. Quantum Electron. QE-18, 1351 (1982); N. Yamada and J. S. Harris, Jr., Appl. Phys. Lett. 60, 2463 (1992)], ordinary tandem coupled-cavity lasers [see N. K. Dutta, G. P. Agrawal, and M. W. Focht, Appl. Phys. Lett. 445 30 (1984)] and vertical-cavity surface-emitting lasers [see D. G. Deppe, C. Lei, T. J. Rogers, and B. G. Streetman, Appl. Phys. Lett. 58, 2616 (1991)].
It is among the further objects of the present invention to provide a semiconductor laser that exhibits relatively large amplitude switching and bistability in its light versus current characteristics.